Variations in the polar cap area during two substorm cycles
Steve Milan,Mark Lester,Stanley W. H. Cowley,Kjellmar Oksavik,Mitchell J. Brittnacher,R. A. Greenwald,George J. Sofko,Jean-Paul Villain +7 more
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In this article, the authors employed observations from several sources to determine the location of the polar cap bound-ary, or open/closed field line boundary, at all local times, allowing the amount of open flux in the magnetosphere to be quantified.Abstract:
This study employs observations from several sources to determine the location of the polar cap bound- ary, or open/closed field line boundary, at all local times, allowing the amount of open flux in the magnetosphere to be quantified. These data sources include global auroral im- ages from the Ultraviolet Imager (UVI) instrument on board the Polar spacecraft, SuperDARN HF radar measurements of the convection flow, and low altitude particle measurements from Defense Meteorological Satellite Program (DMSP) and National Oceanographic and Atmospheric Administration (NOAA) satellites, and the Fast Auroral SnapshoT (FAST) spacecraft. Changes in the open flux content of the mag- netosphere are related to the rate of magnetic reconnection occurring at the magnetopause and in the magnetotail, al- lowing us to estimate the day- and nightside reconnection voltages during two substorm cycles. Specifically, increases in the polar cap area are found to be consistent with open flux being created when the IMF is oriented southwards and low-latitude magnetopause reconnection is ongoing, and de- creases in area correspond to open flux being destroyed at substorm breakup. The polar cap area can continue to de- crease for 100 min following the onset of substorm breakup, continuing even after substorm-associated auroral features have died away. An estimate of the dayside reconnection voltage, determined from plasma drift measurements in the ionosphere, indicates that reconnection can take place at all local times along the dayside portion of the polar cap bound- ary, and hence presumably across the majority of the dayside magnetopause. The observation of ionospheric signatures of bursty reconnection over a wide extent of local times sup- ports this finding.read more
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A decade of the Super Dual Auroral Radar Network (SuperDARN): scientific achievements, new techniques and future directions
Gareth Chisham,Mark Lester,Steve Milan,Mervyn P. Freeman,William A. Bristow,Adrian Grocott,Kathryn A. McWilliams,J. M. Ruohoniemi,Tim K. Yeoman,Peter. Dyson,R. A. Greenwald,Takashi Kikuchi,Michael Pinnock,J.P.S. Rash,Noriaki K. Sato,George J. Sofko,Jean-Paul Villain,Anthony Walker +17 more
TL;DR: The Super Dual Auroral Radar Network (SuperDARN) as discussed by the authors has been operating as an international co-operative organization for over 10 years and has been successful in addressing a wide range of scientific questions concerning processes in the magnetosphere, ionosphere, thermosphere, and mesosphere, as well as general plasma physics questions.
Journal ArticleDOI
Substorm Current Wedge Revisited
Larry Kepko,Robert L. McPherron,Olaf Amm,S. Apatenkov,Wolfgang Baumjohann,J. Birn,Mark Lester,Rumi Nakamura,Tuija Pulkkinen,V. A. Sergeev +9 more
TL;DR: In this article, the substorm current wedge was developed to explain the magnetic signatures observed on the ground and in geosynchronous orbit during substorm expansion, and new observations, including radar and low altitude spacecraft, MHD simulations, and theoretical considerations have tremendously ad-vanced our understanding of this system.
Journal ArticleDOI
Magnetic flux transport in the Dungey cycle: A survey of dayside and nightside reconnection rates
TL;DR: In this paper, changes in the open flux content of the ionospheric polar cap, estimated from auroral, radar, and low-Earth orbit particle measurements, are used to determine dayside and nightside reconnection rates during 73 hours of observation spread over nine intervals.
Journal ArticleDOI
Morphological differences between Saturn's ultraviolet aurorae and those of Earth and Jupiter
John Clarke,Jean-Claude Gérard,Denis Grodent,S. Wannawichian,Jacques Gustin,John E. P. Connerney,F. J. Crary,M. K. Dougherty,William S. Kurth,Stanley W. H. Cowley,Emma J. Bunce,T. W. Hill,Jungeol Kim +12 more
TL;DR: In this article, the authors report ultraviolet images of Saturn, which, when combined with simultaneous Cassini measurements of the solar wind and Saturn kilometric radio emission, demonstrate that its aurorae differ morphologically from those of both Earth and Jupiter.
Journal ArticleDOI
Review of the accomplishments of mid-latitude Super Dual Auroral Radar Network (SuperDARN) HF radars
Nozomu Nishitani,J. M. Ruohoniemi,Mark Lester,J. B. H. Baker,A. V. Koustov,Simon G. Shepherd,Gareth Chisham,Tomoaki Hori,Evan G. Thomas,Roman A. Makarevich,Aurélie Marchaudon,P. V. Ponomarenko,Jim Wild,Stephen E. Milan,William A. Bristow,John Devlin,Ethan S. Miller,R. A. Greenwald,Tadahiko Ogawa,Takashi Kikuchi +19 more
TL;DR: The Super Dual Auroral Radar Network (SuperDARN) is a network of highfrequency (HF) radars located in the high and mid-latitude regions of both hemispheres that is operated under international cooperation as mentioned in this paper.
References
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Excitation and decay of flows in the magnetosphere-ionosphere system due to magnetic reconnection at the dayside magnetopause and in the geomagnetic tail
TL;DR: In this article, the excitation and decay of flows in the magnetosphere-ionosphere system which are caused by magnetic reconnection at the dayside magnetopause and in the geomagnetic tail are applied.
Journal Article
Interhemispheric differences in the HF radar signature of the cusp region: A review through the study of a case example
Steve Milan,Mark Lester +1 more
TL;DR: In this paper, two Super DARN radars were used to observe the conjugate cusp regions during an interval of southward IMF, which allowed to determine several parameters relating to the electrodynamics of the magnetopause reconnection process, including the mean reconnection voltage and the reconnection electric fields and X-line lengths in the two hemispheres.
Journal ArticleDOI
Interplanetary magnetic field By dependence of the relative position of the dayside ultraviolet auroral oval and the HF radar cusp
Kathryn A. McWilliams,Steve Milan,Tim K. Yeoman,John B. Sigwarth,L. A. Frank,Mitchell J. Brittnacher +5 more
TL;DR: In this article, the relative positions of ultraviolet auroral emissions and the HF radar signature of the cusp in the postnoon sector during episodes of flux transfer at the magnetopause were analyzed.
Journal ArticleDOI
A multi-instrument approach to mapping the global dayside merging rate
TL;DR: CUTLASS is supported by the Particle and Astronomy Research Council (PPARC grant PPA/G/O/1999/00 181) and the Finnish Meteorological Institute.